1. Field of the Invention
The present invention relates to a radiation detector that reads out radiation energy as electric signals, and particularly relates to a highly practical radiation detector having a high energy resolution and a high detection efficiency.
2. Description of the Related Art
A radiation detector is a converter that converts radiation energy such as visible lights, infrared rays, ultraviolet rays, X-rays, gamma rays into electric signals. Radiation measurement requires a high energy resolution and a high detection efficiency. A high energy resolution means a small variation in signals obtained from radiation having a certain energy. A high detection efficiency means a high probability that the radiation is irradiated to the detection area of a detector and extracted as signals.
FIG. 13 shows a radiation measuring system using a radiation detector according to the related art. In FIG. 13, an entire board is shown as a radiation detector 21. The radiation detector 21 is connected to an external driving circuit 3 through wires 4 to extract the energy of radiation 1 as electric signals. The radiation detector 21 is provided with a detection area 22 to obtain electric signals when radiation is irradiated to this region. Further, to prevent radiation to a part other than the detection area 22, a collimator 23 having an opening diameter D is provided. The collimator 23 is supported with a distance H from the detection area 22 by a supporter independent from the radiation detector 21.
Signal waveforms obtained by the radiation detector depend on irradiation positions of radiation. The collimator shields irradiation to a part other than the detection area, thus being an effective part for restricting variation in electric signals by irradiation to a part other than the detection area. However, depending on the position relationship between the opening of the collimator and the detection area, irradiation may be shielded by the collimator as the radiation 1A, or may be aside from the detection area 22 as the radiation 1B. To irradiate more radiation to the detection area and obtain a higher detection efficiency, a larger solid angle, which is determined by the opening diameter and the distance between the opening and the detection area, is required. Further, the alignment accuracy of the opening and the detection area, and control of the distance therebetween are significant factors.
Radiation measurement requires a high energy resolution and a high detection efficiency. By installing a collimator to the detection area to narrow the irradiatable region, accurate irradiation to the detection area is achieved. In this case, however, the solid angle determined by the opening diameter of the collimator and the distance between the opening and the detection area is smaller, which causes a problem that a high detection efficiency cannot be obtained.
Further, the alignment accuracy of the opening of the collimator and the detection area is also a factor that restricts the detection efficiency. It is difficult to accurately align a collimator supported by an external supporter with the detection area and control the distance between them, and thus the detection efficiency has not been improved.